Unity UI Shader that hides what is behind it.

Does anyone have a UI shader that essentially cuts a hole in the UI? I tried the DepthMask shader from the wiki with no luck. Everything behind the image would be invisible revealing the camera that is behind.

You can achieve that through various means, wither using a RestMask2D with the appropriate image.
Or alternatively use the Soft Alpha Mask UI component in the Unity UI Extensions project (link in signature) which can use alpha masking to mask an image.

I don't believe a Mask can achieve this effect. To clarify, I am having my Camera's viewport rect conform to a RectTransform as if it were an image itself. This is why I would like my camera to essentially block the UI controls that are behind it.